FUNCTION: This gene encodes a member of the epidermal growth factor (EGF) family and preproprotein that is proteolytically processed to generate a mature protein product. The encoded protein is a ligand of the epidermal growth factor receptor (EGFR) and has been shown to play a role in immunity, inflammation, tissue repair, and lung and mammary gland development. Homozygous knockout mice for this gene exhibit impaired immune system regulation in the skin and gene expression changes characteristic of chronic liver damage. [provided by RefSeq, Aug 2015] PHENOTYPE: Homozygotes for a targeted null mutation exhibit impaired development of mammary gland ducts in pubescent females. Mutant ducts show retarded elongation with few terminal end buds. [provided by MGI curators]